Hospital-acquired infections and codes of practiceSpec 6.15
In short
A hospital-acquired infection is one that a patient gets while in hospital. Causes include vulnerable patients, close contact, invasive procedures, poor hygiene and overuse of antibiotics, which selects for resistant bacteria. Codes of practice limit antibiotic prescribing and set hygiene, isolation and cleaning rules.
A hospital-acquired infection (HAI) is an infection that is acquired in hospital, not present when the patient arrived. Common examples are MRSA (meticillin-resistant Staphylococcus aureus) and Clostridioides difficile (C. difficile).
| Contributory cause | Code of practice |
|---|---|
| Many patients have weakened immune systems (elderly, very young, after surgery, on immunosuppressant drugs) | Isolate vulnerable and infected patients; screen patients for MRSA on admission; protective clothing for staff and visitors |
| Close contact between patients, and staff moving between patients, spreads pathogens by hands and equipment | Hand washing with soap or alcohol gel before and after contact with each patient; bare below the elbow; limited visiting; barrier nursing |
| Open wounds, surgery, catheters, drips and ventilators give pathogens a route into the body | Sterilise surgical instruments; use aseptic technique; remove invasive devices as soon as possible; cover wounds |
| Contaminated surfaces and equipment, and dirty air | Regular cleaning and disinfection; single-use items; good ventilation |
| Overuse and misuse of antibiotics selects for antibiotic-resistant bacteria; killing of gut flora allows C. difficile to grow | Antibiotic stewardship: prescribe only when necessary (never for viral infections); use narrow-spectrum antibiotics where possible; take cultures and test sensitivity first; follow local guidelines; patients take the course exactly as prescribed; keep some antibiotics in reserve |
Hospitals also carry out surveillance (monitoring infection rates and the species involved) so that outbreaks are found early and codes of practice are reviewed.
In a six-mark question, give both parts: cause (for example, 'weakened immune systems') and the matching measure (for example, 'isolate patients'). Marks are for the link.
Quick check
What is the difference between bacteriostatic and bactericidal?
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Bacteriostatic antibiotics stop bacteria growing and dividing. Bactericidal antibiotics kill them.
Why do antibiotics not harm human cells?
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They show selective toxicity: they target structures that bacteria have and human cells lack, such as the peptidoglycan wall and 70S ribosomes.
What is a zone of inhibition?
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The clear area around an antibiotic disc where bacteria cannot grow.
Why is a control disc of sterile water used?
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To show that the disc and water do not themselves stop bacterial growth.
Give two contributory causes of hospital-acquired infections.
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Weakened patients; poor hygiene or contact between patients; use of invasive devices; overuse of antibiotics.
Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026